Math Problem Statement

Five dice were thrown together 96 times. The number of times 4, 5, 6 was actually thrown is given below. Calculate the expected frequency. x ( ) f x 0 1 1 10 2 24 3 35 4 18 5 8

Solution

To calculate the expected frequency for each value of xx, we need to determine the expected probability of getting 4, 5, or 6 on a die in a single throw, and then use that to find the expected number of times each outcome occurs in 96 throws.

The values given appear to be the number of times that 4, 5, or 6 were actually thrown. We also need to calculate the probability of rolling 4, 5, or 6 on a single die.

Step 1: Probability Calculation

On a fair die, there are 6 faces (1 through 6), and each face has an equal chance of being rolled. The probability of rolling either a 4, 5, or 6 in a single throw of one die is:

P(4, 5, or 6)=36=12P(\text{4, 5, or 6}) = \frac{3}{6} = \frac{1}{2}

Thus, the probability of rolling a 4, 5, or 6 on a single die is 12\frac{1}{2}.

Step 2: Expected Frequency Calculation

Now, let’s calculate the expected frequency of throwing 4, 5, or 6 based on 96 trials.

For each number of dice showing a 4, 5, or 6 (denoted by xx), the expected frequency E(fx)E(f_x) is given by:

E(fx)=total number of trials×P(4, 5, or 6 on a die)=96×P(4, 5, or 6)=96×12=48E(f_x) = \text{total number of trials} \times P(\text{4, 5, or 6 on a die}) = 96 \times P(\text{4, 5, or 6}) = 96 \times \frac{1}{2} = 48

Step 3: Interpreting the Data

The frequency distribution f(x)f(x) is given as follows:

xx012345
f(x)f(x)1102435188
  • Total number of occurrences: The sum of all f(x)f(x) values should be equal to the total number of trials (96). Let's check:

1+10+24+35+18+8=961 + 10 + 24 + 35 + 18 + 8 = 96

Thus, the observed data matches the total number of trials.

Step 4: Calculating Expected Frequency for Each xx

The expected frequency for each value of xx (number of dice showing 4, 5, or 6) can be calculated using the binomial distribution, since each die throw is independent.

The number of successes (dice showing 4, 5, or 6) follows a binomial distribution with:

  • n=5n = 5 (the number of dice)
  • p=12p = \frac{1}{2} (the probability of success on each die)

For a binomial distribution, the expected frequency of exactly xx successes is:

E(fx)=(5x)×(12)x×(12)5x×96=(5x)×(12)5×96E(f_x) = \binom{5}{x} \times \left(\frac{1}{2}\right)^x \times \left(\frac{1}{2}\right)^{5-x} \times 96 = \binom{5}{x} \times \left(\frac{1}{2}\right)^5 \times 96

Step 5: Computing the Expected Frequency for Each Value of xx

Now, we compute the expected frequency for each xx from 0 to 5:

  1. For x=0x = 0: E(f0)=(50)×(12)5×96=1×132×96=3E(f_0) = \binom{5}{0} \times \left(\frac{1}{2}\right)^5 \times 96 = 1 \times \frac{1}{32} \times 96 = 3

  2. For x=1x = 1: E(f1)=(51)×(12)5×96=5×132×96=15E(f_1) = \binom{5}{1} \times \left(\frac{1}{2}\right)^5 \times 96 = 5 \times \frac{1}{32} \times 96 = 15

  3. For x=2x = 2: E(f2)=(52)×(12)5×96=10×132×96=30E(f_2) = \binom{5}{2} \times \left(\frac{1}{2}\right)^5 \times 96 = 10 \times \frac{1}{32} \times 96 = 30

  4. For x=3x = 3: E(f3)=(53)×(12)5×96=10×132×96=30E(f_3) = \binom{5}{3} \times \left(\frac{1}{2}\right)^5 \times 96 = 10 \times \frac{1}{32} \times 96 = 30

  5. For x=4x = 4: E(f4)=(54)×(12)5×96=5×132×96=15E(f_4) = \binom{5}{4} \times \left(\frac{1}{2}\right)^5 \times 96 = 5 \times \frac{1}{32} \times 96 = 15

  6. For x=5x = 5: E(f5)=(55)×(12)5×96=1×132×96=3E(f_5) = \binom{5}{5} \times \left(\frac{1}{2}\right)^5 \times 96 = 1 \times \frac{1}{32} \times 96 = 3

Step 6: Conclusion

The expected frequency for each value of xx is:

xx012345
E(fx)E(f_x)3153030153

These are the expected frequencies of throwing 4, 5, or 6 on five dice across 96 throws.

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Math Problem Analysis

Mathematical Concepts

Probability
Binomial Distribution
Expected Value

Formulas

P(4, 5, or 6 on a die) = 1/2
E(f_x) = n * P(4, 5, or 6) = 96 * 1/2 = 48
Binomial Distribution: E(f_x) = C(n, x) * (p^x) * ((1-p)^(n-x)) * total trials

Theorems

Binomial Distribution Theorem

Suitable Grade Level

Grades 10-12